This application claims priority to an application entitled xe2x80x9cMobile Telephone and Antenna thereforxe2x80x9d filed in the Japanese Patent Office on Aug. 31, 1999 and assigned Serial No. 11-246434.
1. Field of the Invention
The present invention relates generally to an antenna for a mobile telephone. In particular, the present invention relates to the structure of a small antenna for use in a mobile telephone.
2. Description of the Related Art
It is known in the art to provide a mobile telephone with either of two types of antennas to transmit and receive radio signals. The first type of antenna is referred to in the art as a xcex/2 type linear antenna (or a half-wavelength antenna), and the second type of antenna is known as an axial mode helical antenna. The helical antenna is made by helically reducing the length of the linear antenna used for an antenna of a mobile telephone. FIGS. 5A and 5B are diagrams illustrating an exterior view of a general mobile telephone.
For example, FIG. 5A illustrates a mobile telephone that has a xcex/2 type linear antenna, and FIG. 5B illustrates a mobile telephone that has a helical antenna. In FIG. 5A, a xcex/2 type linear antenna 42 mounted on a mobile telephone 41 resonates at a designated frequency to generate a vertically polarized plane wave. This antenna structure makes it possible to obtain a non-directional radiation pattern on the vertical plane.
FIG. 6 illustrates a current distribution of the xcex/2 type linear antenna 42. It is clear that the resonant current is concentrated (largest) in the central area of the xcex/2 type linear antenna.
Additionally, the current distribution (radiation pattern) of a helical antenna 44 shown in FIG. 5B, which is mounted on a mobile telephone 43, is equal to that of the xcex/2 type linear antenna shown in FIG. 6. However, the helical antenna 44 is smaller in length than the xcex/2 type linear antenna 42, which makes the helical antenna 44 a more popular choice in mobile telephones than the xcex/2 type linear antenna.
Japanese patent publication No. 7-46026, discloses in detail a small-sized helical antenna, and the contents of this publication should be referred as background material. This helical antenna includes a reflecting plate formed by sequentially disposing a dielectric plate and a strip conductor on a conductive substrate, and the reflecting plate is attached to one end of a helical coil.
For impedance matching, the proper width and length of the conductive substrate and the proper material and thickness of the dielectric plate are selected, thereby to realize the helical antenna which is further reduced in size and has higher performance.
However, when the mobile telephone with the xcex/2 type linear antenna or the helical antenna is operational, the resonant current point shown in FIG. 6 radiates near the head of the user.
FIG. 7 illustrates a state where the user holds the mobile telephone with the conventional xcex/2 type linear antenna to his/her ear. Although the xcex/2 type linear antenna and the helical antenna have slightly different resonant current points, a radiation source 53 is formed near the user""s head 52 when the user holds the mobile telephone 51 to his ear, which exerts radiation waves on the head 52. Recent studies have indicated that the radiation, particularly the transmission from the mobile telephone, may penetrate as much as three inches inside the skull, bombarding a portion of the user""s brain with radiation.
Though not proven, there is an increased concern that the transmission and reception waves of the mobile telephone could exert a harmful influence on the human body. In particular, although not shown in any studies, some researchers are suggesting that long term exposure to the head could affect memory and possibly increase the risk of brain tumors. Accordingly, it is preferable that the radiation source of the antenna should be separated far as possible from the human body as far as possible.
In addition, the non-directional property of the antenna can be degraded when the radiation source of the antenna is formed close to the user""s head because the skull interferes with the radiation.
FIGS. 8A and 8B illustrate radiation patterns of the xcex/2 type linear antenna. Specifically, FIG. 8A illustrates the original radiation pattern of the antenna, and FIG. 8B illustrates a radiation pattern affected by the user""s head. That is, FIG. 8A shows a radiation source 61 of the xcex/2 type linear antenna, which is non-directional on the vertical plane, when the mobile telephone is transmitting or receiving.
As shown in FIG. 8B, since the antenna is so close to the user""s head 62, the head actually functions as a reflecting substance, so that the radio waves will not be radiated to the opposite direction of the head 62. Therefore, the original non-directional property of the antenna, as shown in FIG. 8A, is changed to the directional property shown in FIG. 8B, thus degrading the communication quality.
It is, therefore, an object of the present invention to provide an antenna for a mobile telephone, in which a radiation source of the antenna is separated from the user""s head while the mobile telephone is in use, in order to prevent an influence of the radiation waves on the head and prevent the non-directional property of the radiation pattern from being degraded.
To achieve the above and other objects, a mobile telephone according to the present invention comprises an antenna body for transmitting and receiving radio waves; a terminal for performing communication based on the radio waves transmitted and received by the antenna body; and, a support for maintaining (or supporting) the antenna body to be higher by a predetermined height than the terminal. In this manner, it is possible to improve the directional property of the antenna.
Preferably, the antenna body comprises a cylindrical or circular column-type dielectric substance, and an antenna conductor including a radiation section for radiating the radio waves, which is formed on the longitudinal surface of the dielectric substance. In addition, impedance matching sections are formed on the top and bottom surfaces of the dielectric substance. The antenna body is fixed to be higher than the terminal by a predetermined height when the mobile telephone is in use. That is, by attaching the radiation section of the antenna conductor to the cylindrical or circular column-type dielectric substance, it is possible to provide a very small antenna by the action of the dielectric. Therefore, it is possible to form a radiation source, which is close to the point, and provide a good non-directional property.
Preferably, the antenna body has a specific length such that the transmission and reception waves resonate with the half wavelength (xcex/2), and the radiation section is formed at the center of the antenna body and is fixed in a longitudinal direction of the dielectric substance. In this manner, it is possible to make a very small antenna of about 10 mm.
Preferably, the antenna body is attached to the terminal such that the antenna body should be higher than the top of the user""s head, when the mobile telephone is in use. In this structure, the user""s head is not affected by the radiation waves, and the user""s head does not block radiation of the radio waves, thus preventing degradation of the directional property of the radiation waves. Since the human body is not in the path of the resonant current point of the radio waves of the antenna, it is possible to provide a mobile telephone, which is more safe and sanitary than known in the prior art.
Preferably, the antenna conductor is formed on the dielectric substance by forming a wire pattern by etching, printing or firing. In this way, it is possible to increase productivity and decrease the cost.
Preferably, the dielectric substance is a ceramic. Although inorganic material may also be used for the dielectric substance, it is possible to facilitate evaporation of the antenna conductor and increase the productivity by using the ceramic.
In addition, a rod can be used between a terminal for performing communication based on the radio waves transmitted and received , and that of the antenna body, so that at least during the operation of the mobile telephone by the user, the antenna body is higher than the terminal by a predetermined height. This rod may be a non-radiating and/or non-conductive type of rod. It may be hollow and, for example, a coaxial cable or other conductive material can be arranged therein (or coated in a portion of the interior of the rod, in order to provide a conductive path between the terminal and the antenna body, so that the user""s head does not interfere with the radiation pattern of the antenna.
Further, an antenna for use in a mobile telephone according to the present invention comprises an antenna body of the antenna. The antenna body includes a cylindrical or circular column-type dielectric; and an antenna conductor including a radiation section for radiating the radio waves, formed on the longitudinal surface of the dielectric substance, and impedance matching sections formed on the top and bottom surfaces of the dielectric substance. The antenna body also has a specific length such that transmission and reception waves resonate with the half wavelength (xcex/2), and the radiation section is formed at the center of the antenna body and is fixed in a longitudinal direction of the dielectric substance.
That is, by attaching the radiation section of the antenna conductor to the cylindrical or circular column-type dielectric substance, it is possible to provide a very small antenna by the action of the dielectric. Therefore, it is possible to form a radiation source, which is close to the point, and provide a good non-directional property.